(a) Technical Field
The present invention relates to a hybrid vehicle (or a hybrid electric vehicle), and more particularly, to a method for learning an upwards friction coefficient of an engine clutch of a hybrid vehicle.
(b) Description of the Related Art
An environmentally-friendly vehicle includes a fuel cell vehicle, an electric vehicle, a plug-in electric vehicle, and a hybrid vehicle, and typically includes a motor to generate driving force.
A hybrid vehicle, which is an example of the environmentally-friendly vehicle, uses an internal combustion engine and power of a battery together. In other words, the hybrid vehicle efficiently combines and uses power of the internal combustion engine and power of a motor.
The hybrid vehicle can include an engine, a motor, an engine clutch to adjust power between the engine and the motor, a transmission, a differential gear apparatus, a battery, a starter-generator that starts the engine or generates electricity by output of the engine, and wheels.
Further, the hybrid vehicle can include a hybrid control unit (HCU) for controlling an entire operation of the hybrid vehicle, an engine control unit (ECU) for controlling an operation of the engine, a motor control unit (MCU) for controlling an operation of the motor, a transmission control unit (TCU) for controlling an operation of the transmission, and a battery control unit (BCU) for controlling and managing the battery.
The battery control unit can be called a battery management system (BMS). The starter-generator can be called an integrated starter and generator (ISG) or a hybrid starter and generator (HSG).
The hybrid vehicle can be driven in a driving mode, such as an electric vehicle (EV) mode, which is an electric vehicle mode using only power of the motor, a hybrid vehicle (HEV) mode, which uses rotational force of the engine as main power and uses rotational force of the motor as auxiliary power, and a regenerative braking (RB) mode for collecting braking and inertial energy during driving by braking or inertia of the vehicle through electricity generation of the motor to charge the battery.
It is possible to ensure drivability of the hybrid vehicle by engaging the engine clutch after a speed of the engine and a speed of the motor are synchronized to maintain a constant torque during power transmission between the engine and the motor, when changing from the EV mode to the HEV mode.
However, it is necessary to control the engine clutch to slip and be engaged under driving conditions when the battery is maintained in a low State of Charge (SOC), when the temperatures of the battery and the motor are above a reference temperature condition, and when the road that the vehicle travels on has a steep slope. Additionally, it is necessary to control the pressure of the clutch to control the engine clutch to slip under the driving conditions.
Delivery torque of the engine clutch, which is torque transmitted by physical contact of two friction members that are included in the engine clutch, can be estimated from hydraulic pressure supplied to the engine clutch and the friction coefficient of the friction members.
Controlling the engine clutch is an important factor that determines the drivability and the fuel consumption in operation of the hybrid vehicle. The friction coefficient can be changed by a deviation in hydraulic pressure depending on a current provided to a solenoid valve operating the engine clutch, aging of the solenoid valve, and degradation of the friction members. A change of the friction coefficient can cause a deviation in the delivery torque of the engine clutch.
As described above, it is difficult to precisely control the engine clutch in the hybrid vehicle because a deviation is generated by deterioration of the parts included in the engine clutch, thereby decreasing drivability and fuel economy. Accordingly, it may be necessary to correct the deviation by learning the delivery torque of the engine clutch in the hybrid vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.